Aircraft engine design continually requires components of aircraft engines to have lighter weight materials to increase the aircraft's fuel efficiency and thrust capabilities. In the past, aircraft components have been made with steel. However, steel is relatively heavy and has been replaced with lighter weight high strength materials, such as aluminum or titanium. A further development in producing lightweight parts has resulted in the advent of non-metallic materials, such as composites comprising graphite fibers embedded within a polyimide resin. Composite materials are materials that include embedded fibers inside of a matrix material. The fibers provide reinforcement for the matrix material. The fiber structure prior to being embedded in the matrix is generally referred to as a preform. Graphite fibers embedded within a polyimide resin have drawbacks, including difficulty molding the material into parts, high porosity, microcracking, delamination, and expensive equipment and processes.
A composite fan duct for use in a gas turbine engine is required to have high strength flanges and composite material that is substantially devoid of wrinkles and waves.
Graphite epoxy composite fan ducts have been manufactured using a cross-over tool, disclosed in U.S. Pat. No. 5,145,621 to Pratt (the '621 Patent), which is herein incorporated by reference in its entirety. In the '621 Patent woven graphite fiber preform is mounted on a large spool to form the graphite epoxy composite fan duct. The fibers are situated to provide a flange at either end of the spool. The shape of the spool substantially defines the final shape of the finished composite. The cross-over tool pulls the fibers of the graphite on a spool to provide tension. The tool pulls the fiber through the use of a complex spider tool that encircles the flange portion of the fibers and provides pressure when in combination with three independent vacuum envelopes. The drawbacks of the cross-over tool and method disclosed in the '621 Patent includes a complicated process, and an expensive tool that is difficult to use.
Graphite epoxy composite fan cases have also been manufactured using a mold system utilizing a elastomeric material to assist in providing a force on plies of reinforcing material during manufacture, disclosed in U.S. Pat. No. 5,597,435 to Desautels et al. (the '435 Patent), which is herein incorporated by reference in its entirety. To produce a composite matrix, uncured fiber-reinforced prepreg-type plies (i.e., plies) are mounted onto a mold. Prepreg plies are plies that are impregnated with uncured matrix material before being mounted on the mold. A forcing member and restraining member are placed onto the plies to hold the plies in place. The forcing member is placed between the restraining member and the plies on the mold. The mold, plies, restraining member and forcing member are placed into a furnace and heated. As the assembly is heated, the forcing member uniformly expands and a uniform pressure is applied to the plies. The result is that the plies are compacted as the temperature is raised. The '435 Patent process has the drawback that it only debulks the material and does not pull taut the fabric to provide fiber orientation that provides the finished composite with high strength and uniformity.
Current methods for impregnating matrix material into reinforcing fiber preforms involves placing a matrix material film layer or layers on or within layers of the reinforcing fiber preforms to cover all or the majority of the preform. The entire preform is coated so that during a heated resin infusion phase, the matrix material melts and flows through the thickness of the preform to impregnate it. The impregnation is done using single layer or multiple layers of resin film. The resin film is applied onto the entire surface of the reinforcing fiber preform. Alternatively, the matrix material may be interleaved between layers of the preform to cover all the layers of reinforcing fiber preform. Full coverage of the resin layers on the preform entrap air, volatile material from the matrix material or other gases that may form voids (i.e. void space), which can form undesirable porosity in the body of the cured part. The porosity is particularly undesirable in more complex parts at or near part features. Features include portions of composite material that extend from planar sections of the part. Examples of features include stiffener sections or inserts in gas turbine engine parts. Porosity resulting from void space in the cured reinforced matrix composite may reduce the parts' mechanical properties and may create unacceptable surface features such as pitting. The complete coverage of the reinforcing fiber preform has the additional drawback that the method is difficult to practice and requires a significant amount of time to apply, because the resin must be applied over the entire surface area of the preform.
The present invention solves the problems of the prior art by providing a method and tool that forms the fiber reinforced matrix composite without the disadvantages of the prior art.